Endoscope apparatus

ABSTRACT

An endoscope apparatus includes: a light source device radiating at least one or more illumination lights having a predetermined wavelength band to a subject; a CCD picking up an image of a return light from the subject based on radiation of the illumination light from the light source device; an image processing section outputting a first image signal of a first wavelength band having a peak wavelength of spectral characteristic, between a wavelength band including a maximum value and a wavelength band at a minimum value with regard to an absorption characteristic of living tissue, after image pickup by the CCD; and an observation monitor performing image display on the basis of the first image signal.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of PCT/JP2012/078741filed on Nov. 6, 2012 and claims benefit of Japanese Application No.2012-082288 filed in Japan on Mar. 30, 2012, the entire contents ofwhich are incorporated herein by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an endoscope apparatus, and inparticular to an endoscope apparatus capable of displaying a bloodvessel inside a subject.

2. Description of the Related Art

Conventionally, various kinds of minimally invasive examinations andoperations using an endoscope have been performed in a medical field. Asurgeon can insert an endoscope into a body cavity, observe a subjectwhich has been image-picked up by an image pickup apparatus provided ata distal end portion of an endoscope insertion section, and treats alesioned part using a treatment instrument inserted in a treatmentinstrument channel as necessary. An operation using an endoscope isadvantageous in that a bodily burden on a patient is not heavy becausean abdominal operation is not performed.

An endoscope apparatus is configured including an endoscope, an imageprocessing apparatus connected to the endoscope and an observationmonitor. An image of a legion is picked up by an image pickup deviceprovided at a distal end portion of an endoscope insertion section, andthe image is displayed on the monitor. The surgeon can make a diagnosisor perform necessary treatment, looking at the image displayed on themonitor.

Some endoscope apparatuses are capable of not only performing normallight observation using a white color light but also performing speciallight observation using a special light such as an infrared light inorder to observe an internal blood vessel.

In the case of an infrared endoscope apparatus, for example, indocyaninegreen (ICG) having an absorption peak characteristic in a near infraredlight near a wavelength of 805 nm is injected into a patient's blood asmedicine. Then, infrared lights near wavelengths of 805 nm and 930 nmare radiated to the subject from a light source device in a timedivision manner. A signal of a subject image picked up by a CCD isinputted to a processor of the infrared endoscope apparatus. As for suchan infrared endoscope apparatus, an apparatus is proposed in which theprocessor allocates an image near the wavelength of 805 nm to a greensignal (G) and allocates an image near the wavelength of 930 nm to ablue signal (B), and outputs the images to a monitor as disclosed in,for example, Japanese Patent Application Laid-Open Publication No.2000-41942. Since the image of the infrared light near the image of 805nm which is well-absorbed by the ICG is allocated to green, the surgeoncan observe an infrared image during administration of ICG with highcontrast.

SUMMARY OF THE INVENTION

An endoscope apparatus of an aspect of the present invention is providedwith: an illumination section radiating at least one or moreillumination lights having a predetermined wavelength band to a partunder an epithelium of a living mucosa of a subject; an image pickupsection picking up an image of a return light from the part under theepithelium of the living mucosa based on radiation of the illuminationsection; an image output section outputting a signal corresponding to afirst wavelength band having a narrowband spectral characteristic and asignal corresponding to a second wavelength band having a lowerabsorption coefficient of a hemoglobin absorption characteristic than anabsorption coefficient of a hemoglobin absorption characteristic of thesignal corresponding to the first wavelength band and having such aspectral characteristic that a scattering characteristic of the livingtissue is suppressed, in a red band in a visible range, which is betweena wavelength band including a maximum value and a wavelength bandincluding a minimum value with regard to the hemoglobin absorptioncharacteristic of the living tissue of the subject, after image pickupby the image pickup section; and a display section displaying an imageon the basis of the signal corresponding to the first wavelength bandand the signal corresponding to the second wavelength band.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram showing a configuration of anendoscope apparatus according to a first embodiment of the presentinvention;

FIG. 2 is a diagram showing a configuration of a rotating filter 14according to the first embodiment of the present invention;

FIG. 3 is a diagram for illustrating a whole process flow in narrowbandlight observation according to the first embodiment of the presentinvention;

FIG. 4 is a diagram showing a light absorption characteristic of venousblood according to the first embodiment of the present invention;

FIG. 5 is a diagram for illustrating light propagation volume in livingtissue, of a first narrowband light NL1 (λ1) and a second narrowbandlight NL2 (λ2) according to the first embodiment of the presentinvention;

FIG. 6 is a diagram for illustrating a theoretical basis for a fact thata relatively thick blood vessel existing in a relatively deep part undera living mucosal epithelium can be displayed, according to the firstembodiment of the present invention;

FIG. 7 is a graph showing a function of f according to the firstembodiment of the present invention;

FIG. 8 is a diagram showing the light absorption characteristic ofoxyhemoglobin (HbO₂) and reduced hemoglobin (Hb) according to the firstembodiment of the present invention;

FIG. 9 is a table showing a result of calculation for combinationsbetween cases where diameter of a capillary vessel CB is 0.01 mm and 0.1mm and cases where diameter of a thick blood vessel BV is 1 mm and 2 mm,according to the first embodiment of the present invention;

FIG. 10 is a diagram showing an example of an endoscopic image forillustrating a display example of a blood vessel in an endoscopic imagein a narrowband light observation mode according to the first embodimentof the present invention;

FIG. 11 is a diagram for illustrating an example of an image obtained bypicking up an image of a state of bleeding with a mucosal surfacecovered with blood in the narrowband light observation mode, accordingto the first embodiment of the present invention;

FIG. 12 is a diagram for illustrating the state of bleeding with amucosal surface covered with blood according to the first embodiment ofthe present invention;

FIG. 13 is a diagram for illustrating an example of an image obtained bypicking up an image of a blood puddle portion on a mucosal surface inthe narrowband light observation mode, according to the first embodimentof the present invention;

FIG. 14 is a block diagram for illustrating a configuration of an imageprocessing section 101 according to the first embodiment of the presentinvention;

FIG. 15 is a diagram for illustrating a display example of an endoscopicimage using three image signals according to the first embodiment of thepresent invention;

FIG. 16 is a configuration diagram showing a configuration of anendoscope apparatus 1A according to a second embodiment of the presentinvention;

FIG. 17 is a diagram for illustrating a whole process flow in narrowbandlight observation according to the second embodiment of the presentinvention;

FIG. 18 is a diagram showing a spectral characteristic for illustratinga case of estimating three narrowband-light spectral image signals e1,e2 and e3 from three broadband-light image signals B, G and R accordingto the second embodiment of the present invention;

FIG. 19 is a diagram showing a spectral characteristic for illustratinga case of estimating three narrowband-light spectral estimation imagesignals e1, e21 and e31 from image signals of three narrowband lights,Bn, Gn and Rn according to the second embodiment of the presentinvention;

FIG. 20 is a diagram for illustrating a flow of processing for an imageobtained from an image pickup device 2 in an image processing section101A according to the second embodiment of the present invention;

FIG. 21 is a diagram showing a configuration of a rotating filter 14Aaccording to a third embodiment of the present invention;

FIG. 22 is a diagram for illustrating a whole process flow in a speciallight observation mode according to the third embodiment of the presentinvention;

FIG. 23 is a diagram for illustrating a flow of processing for an imageobtained from an image pickup device 2 in an image processing section101B according to the third embodiment of the present invention;

FIG. 24 is a diagram showing a spectral characteristic for illustratinga case of estimating at least one narrowband-light spectral estimationimage signal e1 from three (or two) broadband-light image signals B, Gand R according to the third embodiment of the present invention;

FIG. 25 is a diagram showing the light absorption characteristic ofvenous blood for illustrating a sixth modification;

FIG. 26 is a diagram for illustrating an example of transition of imagedisplays in enlargement observation in ninth modification;

FIG. 27 is a schematic diagram of an image obtained by photographing aninside of an abdominal cavity of an animal using a spectral endoscopeapparatus capable of radiating a narrowband illumination lightchronologically at intervals of 10 nm of center wavelength; and

FIG. 28 is a graph showing, for multiple monochrome images shown in FIG.27, intensities (logarithmically displayed pixel values) on Line-A ineach image are shown on a vertical axis.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below withreference to drawings.

First Embodiment Configuration of Endoscope Apparatus

An embodiment of the present invention will be described below withreference to drawings.

First, a configuration of an endoscope apparatus according to thepresent embodiment will be described. FIG. 1 is a configuration diagramshowing the configuration of the endoscope apparatus according to thepresent embodiment.

As shown in FIG. 1, an endoscope apparatus 1 of the present embodimentis configured with an electronic endoscope 3 having a CCD 2, which is animage pickup device, as biological image information acquiring means ora living body image information acquiring section to be inserted into abody cavity to pick up an image of intra-body cavity tissue, a lightsource device 4 which supplies an illumination light to the electronicendoscope 3, and a video processor 7 which performs signal processing ofan image pickup signal from the CCD 2 of the electronic endoscope 3 anddisplays an endoscopic image on an observation monitor 5. The endoscopeapparatus 1 has two modes of a normal light observation mode and anarrowband light observation mode. Note that, in the description below,since the normal light observation mode of the endoscope apparatus 1 isthe same as a conventional normal light observation mode, description ofa configuration of the normal light observation mode is omitted, and thenarrowband light observation mode will be mainly described.

The CCD 2 constitutes an image pickup section or image pickup means forreceiving a return light of an illumination light radiated to a subjectto pick up an image of the subject.

The light source device 4 as illumination means is configured beingprovided with a xenon lamp 11 which emits an illumination light (whitecolor light), a heat ray cut filter 12 which cuts off a heat ray of thewhite color light, a diaphragm device 13 which controls a light amountof the white color light via the heat ray cut filter 12, a rotatingfilter 14 as band limiting means or a band limiting section which causesthe illumination light to be frame-sequential lights, a condensing lens16 which collects the frame-sequential lights via the rotating filter 14on an incident face of a light guide 15 arranged in the electronicendoscope 3, and a control circuit 17 which controls rotation of therotating filter 14. The xenon lamp 11, the rotating filter 14 and thelight guide 15 constitute an irradiating section or irradiating meansthat illuminates the subject with the illumination light.

FIG. 2 is a diagram showing a configuration of the rotating filter 14.The rotating filter 14 is a filter which transmits a light from thexenon lamp 11 which is a light source. The rotating filter 14 as awavelength band limiting section or wavelength band limiting means isconfigured in a disc shape as shown in FIG. 2 and with a structurehaving a rotating shaft at the center. The rotating filter 14 has twofilter groups. On an outer circumferential side of the rotating filter14, an R (red) filter section 14 r, a G (green) filter section 14 g anda B (blue) filter section 14 b constituting a filter set for outputtingframe-sequential lights having a spectral characteristic for normallight observation are arranged along a circumferential direction as afirst filter group.

On an inner circumferential side of the rotating 14, three filters14-600, 14-630 and 14-540 that transmit lights having threepredetermined narrowband wavelengths are arranged along thecircumferential direction as a second filter group.

The filter 14-600 is configured to transmit a light near a wavelength of600 nm (λ1) as a narrowband light. The filter 14-630 is configured totransmit a light near a wavelength of 630 nm (λ2) as a narrowband light.The filter 14-540 is configured to transmit a light near a wavelength of540 nm (λ1) as a narrowband light.

In the case of near the wavelength of 600 nm, “near” means that thelight is a narrowband light having a center wavelength of 600 nm andhaving a distribution in a range of a width of, for example, 20 nm withthe wavelength of 600 nm as the center (i.e., from a wavelength of 590nm before the wavelength of 600 nm to a wavelength of 610 nm after thewavelength of 600 nm). The same goes for the other wavelengths, thewavelength of 630 nm and the wavelength of 540 nm to be described later.

The rotating filter 14 is arranged on an optical path extending from thexenon lamp 11, which is a section of emitting an illumination light, toan image pickup surface of the CCD 2. The rotating filter 14 limits atleast one (here, three) wavelength band among multiple wavelength bandsof the illumination light to be narrowed in each mode.

The control circuit 17 controls a motor 18 for causing the rotatingfilter 14 to rotate to control the rotation of the rotating filter 14.

A rack 19 a is connected to the motor 18. A motor not shown is connectedto a pinion 19 b. The rack 19 a is attached to be screwed with thepinion 19 b. The control circuit 17 can move the rotating filter 14 in adirection indicated by an arrow d by controlling rotation of the motorconnected to the pinion 19 b. Therefore, the control circuit 17 controlsthe motor connected to the pinion 19 b so that, according to a modeswitching operation by the user to be described later, the first filtergroup is positioned on the optical path in the normal light observationmode, and the second filter group in the narrowband light observationmode.

Note that, electric power is supplied from a power supply section 10 tothe xenon lamp 11, the diaphragm device 13, the rotating filter motor18, and the motor (not shown) connected to the pinion 19 b.

Thus, the light source device 4 constitutes illumination means or anillumination section that radiates at least one or more illuminationlights (here, three narrowband lights) having a predetermined wavelengthband to a subject in the narrowband light observation mode. Here, one ofthe three illumination lights is a narrowband light for clearlydisplaying a blood vessel in a deep part 1 to 2 mm from a mucosalepithelium part, and the other two are a narrowband light for displayinga blood vessel in a deeper part and a narrowband light for displayingcapillary vessels within a range near the epithelium part. Therefore,the light source device 4 is the illumination means or the illuminationsection that radiates at least one or more illumination lights via theband limiting means or the band limiting section that limits awavelength band to a first wavelength band (to be described later) inthe narrowband light observation mode.

The video processor 7 includes a CCD driving circuit 20 which is a CCDdriver, an amplifier 22, a process circuit 23, an A/D converter 24, awhite balance circuit (hereinafter referred to as W. B) 25, a selector100, an image processing section 101, a selector 102, a γ correctioncircuit 26, an enlargement circuit 27, an emphasis circuit 28, aselector 29, synchronizing memories 30, 31 and 32, and 33, an imageprocessing circuit 33, D/A converters 34, 35 and 36, a timing generator(hereinafter referred to as T. G) 37, a mode changeover circuit 42, alight-adjusting circuit 43, a light adjustment control parameterchangeover circuit 44, a control circuit 200, and a combination circuit201 as display image generating means or a displayed image generatingsection.

The CCD driving circuit 20 drives the CCD 2 provided in the electronicendoscope 3 and causes the CCD 2 to output frame-sequential image pickupsignals synchronized with rotation of the rotating filter 14. Theamplifier 22 amplifies the frame-sequential image pickup signalsobtained by picking up an image of intra-body cavity tissue by the CCD 2via an objective optical system 21 provided at a distal end of theelectronic endoscope 3.

Note that a polarizing plate may be arranged on each of a front face ofthe CCD 2, which is an image pickup device, and a front face of thelight guide 15, in a crossed Nichol prism state. By two polarizing endsin the crossed Nichol prism state, the CCD 2 can pick up an image of alight mainly from a deep mucosa without receiving a light reflected froma mucosal surface.

The process circuit 23 performs correlated double sampling, noiseremoval and the like for the frame-sequential image pickup signals viathe amplifier 22. The A/D converter 24 converts the frame-sequentialimage pickup signals having passed through the process circuit 23 todigital frame-sequential image signals.

The W. B 25 performs gain adjustment and executes white balanceprocessing for the frame-sequential image signals digitized by the A/Dconverter 24 so that, for example, brightness of an R signal of theimage signal and brightness of a B signal of the image signal are equalwith each other with reference to a G signal of the image signal.

Note that white balance adjustment at the W.B 25 is performed withreference to luminance of a return light of a narrowband light near thewavelength of 600 nm.

The selector 100 distributes and outputs frame-sequential image signalsfrom the W. B 25 to respective sections in the image processing section101.

The image processing section 101 is an image signal processing sectionor image signal processing means that converts an RGB image signal fornormal light observation or three image signals for narrowband lightobservation from the selector 100 to an image signal for display. Theimage processing section 101 outputs, according to a selection signal SSfrom the control circuit 200 based on a mode signal, image signals inthe normal light observation mode and in the narrowband lightobservation mode to the selector 102.

The selector 102 sequentially outputs frame-sequential image signals ofthe image signal for normal light observation and the image signal fornarrowband light observation from the image processing section 101 tothe γ correction circuit 26 and the combination circuit 201.

The γ correction circuit 26 applies γ correction processing to theframe-sequential image signals from the selector 102 or the combinationcircuit 201. The enlargement circuit 27 performs enlargement processingof the frame-sequential image signals which have beenγ-correction-processed by the γ correction circuit 26. The emphasiscircuit 28 applies edge emphasis processing to the frame-sequentialimage signals which have been enlargement-processed by the enlargementcircuit 27. The selector 29 and the synchronizing memories 30, 31 and 32are for synchronizing the frame-sequential image signals from theemphasis circuit 28.

The image processing circuit 33 reads out respective frame-sequentialimage signals stored in the synchronizing memories 30, 31 and 32 andperforms moving image color shift correction processing and the like.The D/A converters 34, 35 and 36 convert the image signals from theimage processing circuit 33 into RGB analog video signals and output theRGB analog video signals to the observation monitor 5. The T. G 37inputs a synchronization signal synchronized with the rotation of therotating filter 14, from the control circuit 17 of the light sourcedevice 4, and outputs various timing signals to the respective circuitsin the video processor 7 described above.

In the electronic endoscope 2, a mode changeover switch 41 for switchingbetween the normal light observation mode and the narrowband lightobservation mode is provided. An output of this mode changeover switch41 is outputted to the mode changeover circuit 42 in the video processor7. The mode changeover circuit 42 of the video processor 7 outputs acontrol signal to a light adjustment control parameter changeovercircuit 44 and the control circuit 200. The light-adjusting circuit 43controls the diaphragm device 13 of the light source device 4 on thebasis of light adjustment control parameters from the light adjustmentcontrol parameter changeover circuit 44 and an image pickup signal whichhas passed through the process circuit 23 to perform proper brightnesscontrol.

Each circuit in the video processor 7 executes predetermined processingcorresponding to a specified mode. Processing corresponding to each ofthe normal light observation mode and the narrowband light observationmode is executed, and an image for normal light observation or an imagefor narrowband light observation is displayed on the observation monitor5. The observation monitor 5 is display means or a display section thatdisplays an image on the basis of an image signal of a relatively thickblood vessel with a diameter of about 1 to 2 mm in a deep mucosa about 1to 2 mm from a mucosal epithelium part.

(Whole Process Flow of Narrowband Light Observation)

Next, an overall rough flow of the narrowband light observation in thepresent embodiment will be briefly described below.

FIG. 3 is a diagram for illustrating a whole process flow in thenarrowband light observation according to the present embodiment.

A surgeon inserts the insertion section of the endoscope into a bodycavity and positions the distal end portion of the insertion section ofthe endoscope near a lesioned part under the normal light observationmode. When confirming the treatment target lesioned part, the surgeonoperates the mode changeover switch 41 to switch the endoscope apparatus1 to the narrowband light observation mode in order to observe arelatively thick blood vessel in a deep part having a diameter of, forexample, 1 to 2 mm, and running from a submucosa to a muscularispropria.

Under the narrowband light observation mode, the control circuit 17 ofthe endoscope apparatus 1 controls the motor connected to the pinion 19b to move the position of the rotating filter 14 so that a lighttransmitted through the second filter group is emitted from the lightsource device 4. Furthermore, the control circuit 200 also controls thevarious circuits in the video processor 7 to perform image processingfor observation by a narrowband wavelength.

As shown in FIG. 3, in the narrowband light observation mode, anillumination light having a narrowband wavelength is emitted from thedistal end portion of the insertion section of the endoscope 3, from anillumination light generating section 51, transmitted through a stratummucosum, and radiated to a blood vessel 61 running in a submucosa and amuscularis propria. Here, the illumination light generating section 51is configured including the light source device 4, the rotating filter14, the light guide 15, and the like, and emits an illumination lightfrom the distal end of the endoscope insertion section. By rotation ofthe rotating filter 14, a narrowband light near the wavelength of 600nm, a narrowband light near the wavelength of 630 nm and a narrowbandlight near the wavelength of 540 nm are successively and sequentiallyemitted from the light source device 4 and radiated to a subject.

Each of reflected lights of the narrowband light near the wavelength of600 nm, the narrowband light near the wavelength of 630 nm and thenarrowband light near the wavelength of 540 nm is received by areflected light receiving section 52 which is the CCD 2. The CCD 2outputs image pickup signals of the respective reflected lights, andsupplied to the selector 100 via the amplifier 22 and the like. Theselector 100 holds a first image signal P1 near the wavelength of 600nm, a second image signal P2 near the wavelength of 630 nm and a thirdimage signal P3 near the wavelength of 540 nm and supplies the images tothe image processing section 101 according to a predetermined timingfrom the T. G 37. The image processing section 101 includes a colorconversion processing section 101 b for the narrowband light observationmode.

For example, in ESD in which, for example, a stratum mucosum of an innerwall of a digestive tract such as a stomach, a gullet and a large bowel,where a lesioned part exists, is dissected and ablated with the use ofthe endoscope apparatus 1, the surgeon has to be careful not to cut arelatively thick blood vessel in tissue with an electric surgical knifeor the like. When setting the endoscope apparatus 1 to the narrowbandlight observation mode, the surgeon can clearly depict blood vesselsunder the surface of living tissue.

The color conversion processing section 101 b of the image processingsection 101 in FIG. 1 allocates each image signal to each channel of RGBof the observation monitor 5 and supplies the image signal to theselector 102. As a result, the relatively thick blood vessel 61 in adeep mucosa is displayed with high contrast on a screen 5 a of theobservation monitor 5. Thereby, the surgeon can apply the ESD to thelesioned part while paying attention to the blood vessel 61 running inthe submucosa and the muscularis propria, which is displayed on theobservation monitor 5.

Here, a light absorption characteristic of venous blood will bedescribed. FIG. 4 is a diagram showing the light absorptioncharacteristic of venous blood. A vertical axis in FIG. 4 indicates amolar absorption coefficient (cm⁻¹/M) and a horizontal axis indicateswavelength. Note that, though illumination lights of the threenarrowband lights are influenced by a scattering characteristic ofliving tissue itself, the scattering characteristic of the living tissueitself decreases almost monotonously relative to increase in wavelength,and, therefore, FIG. 4 will be described as a diagram of the lightabsorption characteristic of the living tissue.

In general, venous blood includes oxyhemoglobin (HbO₂) and reducedhemoglobin (Hb) (hereinafter, generically referred to simply ashemoglobin) at the rate of about 60:40 to 80:20. Light is absorbed byhemoglobin, but the absorption coefficient differs according to lightwavelength. FIG. 4 shows the light absorption characteristic of venousblood for each wavelength from 400 nm to about 800 nm, and, within arange from 550 nm to 750 nm, the absorption coefficient shows a maximumvalue at a point of a wavelength of about 576 nm, and a minimum value ata point of a wavelength of about 730 nm.

In the narrowband light observation mode, three narrowband lights areradiated, and each return light is received by the CCD 2.

A narrowband light near the wavelength of 600 nm (hereinafter referredto as a first narrowband light NL1) is a light of a wavelength bandwithin a wavelength band R from a maximum value ACmax of the absorptioncharacteristic of hemoglobin (here, an absorption coefficient at thewavelength of 576 nm) to a minimum value ACmin (here, an absorptioncoefficient at the wavelength of 730 nm).

A narrowband light near the wavelength of 630 nm (hereinafter referredto as a second narrowband light NL2) is also a light within thewavelength band R from the maximum value ACmax of the absorptioncharacteristic of hemoglobin to the minimum value ACmin However, it is alight of a wavelength band longer than the wavelength of the firstnarrowband light NL1 with a lower absorption coefficient in which thescattering characteristic of living tissue is suppressed. That thescattering characteristic is suppressed means that the scatteringcoefficient decreases toward the long wavelength side.

That is, the light source device 4 radiates the first illumination lightNL1 having a peak wavelength of spectral characteristic between awavelength band that includes the maximum value ACmax and a wavelengthband at the minimum value ACmin in the absorption characteristic ofliving tissue.

Furthermore, here, the light source device 4 also radiates a secondillumination light NL2 having a lower value of the absorptioncharacteristic than the image signal P1 by the first illumination lightNL1 and having a peak wavelength of such a spectral characteristic thatthe scattering characteristic of living tissue is suppressed.

Furthermore, the light source device 4 also radiates a narrowband lightnear the wavelength of 540 nm (hereinafter referred to as a thirdnarrowband light NL3). The third narrowband light NL3 is a light of awavelength band outside the wavelength band R from the maximum valueACmax to minimum value ACmin of the absorption characteristic ofhemoglobin, which is an illumination light which can be transmitted by apredetermined distance from an epithelium of a mucosal surface of asubject.

The CCD 2 outputs an image pickup signal of each of images of the threenarrowband lights. Therefore, each image includes multiple pixel signalsbased on each of return lights of the first, second and third narrowbandlights NL1, NL2 and NL3.

Furthermore, light propagation in living tissue of the first and secondnarrowband lights NL1 and NL2 which are illumination lights will bedescribed.

FIG. 5 is a diagram for illustrating light propagation volume in livingtissue of the first narrowband light NL1 (λ1) and the second narrowbandlight NL2 (λ2). Each of the first and second narrowband lights NL1 andNL2 repeats multiple scattering processes in living tissue, and, as aresult, emitted from a mucosal surface as return lights. The first andsecond narrowband light NL1 and NL2 have mean free paths MFP1 and MFP2,respectively. The mean free path MFP1 of the first narrowband light NL1is shorter than the mean free path MFP2 of the second narrowband lightNL2.

As shown in FIG. 5, the first narrowband light NL1 near the wavelengthof 600 nm (λ1) reaches the vicinity of the blood vessel 61, and thesecond narrowband light NL2 near the wavelength 630 nm (λ2) reaches aposition slightly deeper than the blood vessel 61. Therefore, by usingthis first narrowband light NL1, it becomes possible to display arelatively thick blood vessel with a diameter of 1 to 2 mm existing in arelatively deep part 1 to 2 mm under a living mucosal epithelium.

Furthermore, as described later, a thicker blood vessel in a deeper partcan be displayed by the second narrowband light NL2 near the wavelengthof 630 nm (λ2).

Here, description will be made on a theoretical basis for the face that,by using this first narrowband light NL1 near the wavelength of 600 nm(λ1), it becomes possible to display a relatively thick blood vesselexisting in a relatively deep part under a living mucosal epitheliumwith high contrast.

FIG. 6 is a diagram for illustrating a theoretical basis for the factthat it becomes possible to display a relatively thick blood vesselexisting in a relatively deep part under a living mucosal epithelium. InFIG. 6, a relatively thick blood vessel is denoted by BV, and acapillary vessel is denoted by CB.

Here, a simplified model is assumed in which a return light for anincident light is assumed to be a transmitted light for the incidentlight, and such a wavelength is determined that the amount of light ofthe return light is maximized for the capillary vessel.

As shown in FIG. 6, when the capillary vessel CB is a medium, atransmittance which is a ratio of output light intensity I_(L) to inputlight intensity I_(O) of a light inputted to the capillary vessel CB isshown by a following equation (1) from the Beer-Lambert law:

$\begin{matrix}{\frac{I_{L}}{I_{0}} = {\exp \left( {{- \mu}\; L} \right)}} & {{Equation}\mspace{14mu} (1)}\end{matrix}$

Here, L[m] indicates a propagation distance (meter), which is a diameterof the capillary vessel CB; L>O is satisfied; μ[m⁻¹] is a coefficient ofabsorption per unit meter; and μ>O is satisfied.

Similarly, as shown in FIG. 6, a transmittance, which is a ratio ofoutput light intensity I_(mL) to input light intensity I_(O) inputted tothe blood vessel BV with a diameter mL, is shown by a following equation(2):

$\begin{matrix}{\frac{I_{mL}}{I_{0}} = {\exp \left( {{- \mu}\; m\; L} \right)}} & {{Equation}\mspace{14mu} (2)}\end{matrix}$

Here, as for m, m>1 is satisfied, and mL[m] indicates a propagationdistance (meter) which is a diameter of the blood vessel BV.

A difference f(μ) between a transmittance for the propagation distance Land a transmittance for the propagation distance mL is indicated by afollowing equation (3) from the above equations (1) and (2).

$\begin{matrix}{{f(\mu)} = {{\frac{I_{L}}{I_{0}} - \frac{I_{mL}}{I_{0}}} = {{\exp \left( {{- \mu}\; L} \right)} - {\exp \left( {{- \mu}\; m\; L} \right)}}}} & {{Equation}\mspace{14mu} (3)}\end{matrix}$

The difference f(μ) between the transmittances always takes a positivevalue. By differentiating both sides of this equation (3) with μ, theequation (3) is arranged like a following equation (4):

$\begin{matrix}\begin{matrix}{\frac{f}{\mu} = {{{- L}\mspace{14mu} {\exp \left( {{- \mu}\; L} \right)}} + {{mL}\mspace{14mu} {\exp \left( {{- \mu}\; m\; L} \right)}}}} \\{= {L\left\{ {{m\mspace{14mu} {\exp \left( {{- \mu}\; m\; L} \right)}} - {\exp \left( {{- \mu}\; L} \right)}} \right\}}}\end{matrix} & {{Equation}\mspace{14mu} (4)}\end{matrix}$

It is when the condition of a following equation (5) is satisfied thatthe right side of the equation (4) becomes 0. After transition from theequation (5) to an equation (6), the condition is indicated by anequation (7).

$\begin{matrix}{{\exp \left( {{- \mu}\; L} \right)} = {m\mspace{14mu} {\exp \left( {{- \mu}\; m\; L} \right)}}} & {{Equation}\mspace{14mu} (5)} \\{{{- \mu}\; L} = {{\ln (m)} - {\mu \; m\; L}}} & {{Equation}\mspace{14mu} (6)} \\{\mu = \frac{\ln (m)}{\left( {m - 1} \right)L}} & {{Equation}\mspace{14mu} (7)}\end{matrix}$

When the value of μ shown in the equation (7) is taken, f takes amaximum value, that is, the contrast of the blood vessel BV shows amaximum value.

Here, when the equation (7) is substituted into the equation (3), themaximum value f_(max) of f becomes a value shown by a following equation(8).

$\begin{matrix}{f_{\max} = {{\exp\left( {- \frac{\ln (m)}{m - 1}} \right\}} - {\exp \left\{ {- \frac{m\; {\ln (m)}}{m - 1}} \right\}}}} & {{Equation}\mspace{14mu} (8)}\end{matrix}$

FIG. 7 is a graph showing a function of f. As shown in FIG. 7, it isnecessary to select the absorption coefficient μ in the equation (7) inorder to maximize the transmittances of two transmitted lights withdifferent optical path differences.

When μ_(a)[m⁻¹M⁻¹] indicates an absorption coefficient per mol, and c[M]indicates concentration (mol) (a mol absorption coefficient) of anabsorbing substance, the equation (1) is indicated by a followingequation (9).

μ=cμ _(a)  Equation (9)

The absorption coefficient per mol μ_(a)[m⁻¹M⁻¹] is indicated by afollowing equation (10), from the equations (7) and (9). In this case, ftakes the maximum value f_(max).

$\begin{matrix}{\mu_{a} = \frac{\ln (m)}{\left( {m - 1} \right){cL}}} & {{Equation}\mspace{14mu} (10)}\end{matrix}$

For example, when two kinds of blood vessels, such a capillary vessel CBthat L is 0.1 mm (that is, the diameter is 0.1 mm) and such a thickblood vessel BV that m is 10 (that is, the diameter is 1 mm), areassumed, c is estimated to be about 2.0×10⁻³ [M] from a standard valueof hemoglobin concentration. Note that it is assumed that a standardvalue of male hemoglobin concentration is 12.4 to 17.0 g/dl, andmolality of hemoglobin is 6.6×10⁴ g/mol.

When this value is substituted into the equation (10), the absorptioncoefficient μ_(a)[m⁻¹M⁻¹] is as indicated by a following equation (11).

$\begin{matrix}\begin{matrix}{\mu_{a} \approx \frac{\ln (10)}{\left( {10 - 1} \right) \times 2 \times 10^{- 3} \times 10^{- 4}}} \\{= {1.3 \times {10^{6}\left\lbrack {m^{- 1}M^{- 1}} \right\rbrack}}} \\{= {1.3 \times {10^{4}\left\lbrack {{cm}^{- 1}M^{- 1}} \right\rbrack}}}\end{matrix} & {{Equation}\mspace{14mu} (11)}\end{matrix}$

In FIG. 4, such a wavelength that a value of the vertical axis becomesthe value of the equation (11) is about 600 nm That is, by using thefirst narrowband light NL1 with the wavelength of 600 nm (λ1), itbecomes possible to display a relatively thick blood vessel existing ina relatively deep part under a living mucosal epithelium with highcontrast.

As described above, the wavelength band of the first narrowband lightNL1 is a wavelength band where difference between light transmittancesof a capillary vessel under a living mucosa of a subject and a bloodvessel having a diameter longer than that of the capillary vessel is apredetermined value or more. FIG. 8 is a diagram showing the lightabsorption characteristics of oxyhemoglobin (HbO₂) and reducedhemoglobin (Hb). In FIG. 8, a solid line graph indicates the absorptioncharacteristic of oxyhemoglobin (HbO₂), and a dashed-dotted line graphindicates the absorption characteristic of reduced hemoglobin (Hb). FromFIG. 8, it is seen that the wavelength satisfying the above equation(11) is about 590 nm indicated by a point of PP1 in the case ofoxyhemoglobin (HbO₂) and about 602 nm indicated by a point of PP2 in thecase of reduced hemoglobin (Hb). Note that it is necessary to payattention to the fact that, though an optical path length corresponds tothickness of a blood vessel when there is not light scattering, anoptical path length does not correspond to thickness of a blood vesselwhen light scattering cannot be ignored.

There is variation in diameters of the blood vessel BV in a deep partand the capillary vessel CB in an epithelium. Therefore, calculationsimilar to the above has been performed for a case where each of thediameters of the blood vessel BV in a deep part and the capillary vesselCB in an epithelium are changed.

FIG. 9 is a table showing a result of calculation for combinationsbetween cases where diameter of the capillary vessel CB is 0.01 mm and0.1 mm and cases where diameter of the thick blood vessel BV is 1 mm and2 mm From FIG. 9, it is seen that the wavelength satisfying the equation(11) is, as an average value, about 590 nm in the case of oxyhemoglobin(HbO₂) and about 603 nm in the case of reduced hemoglobin (Hb).

A minimum wavelength in FIG. 9 is 586 nm, and a maximum wavelength is614 nm Therefore, from FIG. 9, a range of light in which a relativelythick blood vessel can be displayed with high contrast is from 585 nm,which is the minimum wavelength, to 615 nm, which is the maximumwavelength. That is, by using a narrowband light within a range from 15nm before and 15 nm after the wavelength of 600 nm, within a rangeindicated by dotted lines in FIG. 8, a relatively thick blood vessel canbe displayed with high contrast.

FIG. 27 is a schematic diagram of an image obtained by photographing aninside of an abdominal cavity of an animal using a spectral endoscopeapparatus capable of radiating a narrowband illumination lightchronologically at intervals of 10 nm of center wavelength. Morespecifically, FIG. 27 shows an image in which monochrome images of 540nm, 600 nm and 630 nm are allocated to a B channel, a G channel and an Rchannel, respectively. A blood vessel V1 and a blood vessel V2 in theimage are thick blood vessels running from an upper left direction to alower right direction in the image. The blood vessel V1 is positioneddeeper from a mucosal surface than the blood vessel V2. Here, monochromeimages of a total of fifteen patterns have been photographed at 10nm-step intervals from 540 nm over to 680 nm.

FIG. 28 is a graph showing, for the multiple monochrome images shown inFIG. 27, intensities (logarithmically displayed pixel values) on Line-Ain each image are shown on a vertical axis. A horizontal axis in FIG. 28indicates positions of pixels on Line-A in each image. Positions ofpixels of the blood vessel V1 are near 25 to 50, and positions of pixelsof the blood vessel V2 are near 75 to 110. It is seen from FIG. 28 thatan illumination wavelength the intensity of which decreases in both ofthe blood vessel V2 existing in a relatively shallow part and the bloodvessel V1 positioned in a deep part, that is, a wavelength in which anillumination light is strongly absorbed in the blood vessels V1 and V2is about 590 to 620 nm.

Therefore, in order to detect a blood vessel existing from a relativelyshallow part to a deep part, an about 590 to 620 nm narrowband light isimportant wavelength information. The blood vessel V1 exists in a partabout 1 to 2 mm deep from a mucosal surface. Note that a result of thisexperiment almost corresponds to a result of the theoretical calculationby the Beer-Lambert law described before (a relatively thick bloodvessel can be displayed with high contrast by using a narrowband lightwithin a range from 15 nm before and 15 nm after the wavelength of 600nm).

As described above, the illumination means or the illumination sectionthat includes the light source device 4 to display a thick blood vesselin a relatively deep part from a living mucosal epithelium with goodcontrast radiates the narrowband light NL1 which is an illuminationlight having a peak wavelength of spectral characteristic between awavelength band including the maximum value ACmax and a wavelength bandat the minimum value ACmin in the absorption characteristic of livingtissue.

Note that, though an image signal of a narrowband light near thewavelength of 600 nm is generated here, it is possible to display ablood vessel in a deep mucosa by generating an image signal having apredetermined wavelength width and having a peak wavelength of spectralcharacteristic between a wavelength band which includes a maximum valueand a wavelength band at a minimum value in the absorptioncharacteristic of living tissue as shown in FIG. 4 because there isvariation among diameters of blood vessels and there are various depthsas described above.

Furthermore, the light source device 4 also radiates the narrowbandlight NL2 having a lower value in the absorption characteristic of areturn light by the first narrowband light NL1, having a peak wavelengthof spectral characteristic in which a scattering characteristic ofliving tissue is suppressed, and being an illumination light of awavelength band different from the wavelength band of the firstnarrowband light NL1, and the third narrowband light NL3 that can betransmitted by a predetermined distance from a subject's epithelium.

The narrowband light NL2 is a narrowband light for obtaining an image ofa blood vessel in a deeper part than a blood vessel displayed with thenarrowband light NL1, and the third narrowband light NL3 is a narrowbandlight for obtaining an image of a capillary vessel in an epithelium.

Next, processing in the image processing section 101 will be described.FIG. 10 is a diagram showing an example of an endoscopic image forillustrating a display example of a blood vessel in an endoscopic imagein the narrowband light observation mode.

In the normal light observation mode, in a picked-up endoscopic imageEI, a blood vessel in a deep part 1 to 2 mm from an epithelium is notdisplayed or is difficult to be displayed on the endoscopic image EI onthe observation monitor 5.

In comparison, in the narrowband light observation mode, when adeep-part blood vessel exists in the picked-up endoscopic image EI, theblood vessel 61 is displayed on the endoscopic image EI as shown in FIG.10.

Thus, the image processing section 101 constitutes image output means oran image output section for, after image pickup by the image pickupmeans or the image pickup section, outputting an image signal P1 (λ1) ofa predetermined wavelength band having a peak wavelength of spectralcharacteristic between a wavelength band including the maximum valueACmax and a wavelength band at the minimum value ACmin in the absorptioncharacteristic of living tissue.

According to an experiment performed by the applicant, when an image isgenerated with the use of the narrowband light NL1 as described above,it is possible not only to display a relatively thick blood vessel in adeep mucosa but also to display a state of a flow of bleeding in a statethat a mucosal surface is covered with blood due to the bleeding from amucosa.

Conventionally, in white color light observation, when a mucosal surfaceis covered with blood, a place where bleeding occurs, that is, ableeding point cannot be seen, and, therefore, the surgeon cannotperform treatment to stop the bleeding quickly. In comparison, accordingto the present embodiment, since it becomes easier to find the bleedingpoint on the mucosal surface under the blood, the surgeon can performhemostasis treatment quickly.

FIG. 11 is a diagram for illustrating an example of an image obtained bypicking up an image of a state of bleeding with a mucosa covered withblood in the narrowband light observation mode. FIG. 12 is a diagram forillustrating the state of bleeding with a mucosal surface covered withblood.

As shown in FIG. 11, there may be a case where a mucosal surface 71 a iscovered with blood 73 (indicated by dotted lines) of bleeding from ableeding point 72 on the mucosal surface 71 a of a mucosa 71. When theblood 73 is observed in the narrowband light observation mode describedabove, a narrowband light near the wavelength of 600 nm is transmittedthrough the blood 73, and blood flowing from the bleeding point 72 onthe mucosal surface 71 a is displayed, as shown in FIG. 11. This isbecause density (that is, concentration) of blood spouting from thebleeding point 72 is high in the vicinity of the bleeding point 72.Therefore, it is possible to visually confirm a flow of blood BF flowingfrom the bleeding point 72 and, therefore, identify the bleeding point72 under the blood 73, and the surgeon can quickly perform hemostasistreatment for the bleeding point 72, which leads to shortening of anoperation time period.

Furthermore, when an image is generated with the use of the narrowbandlight NL1 as described above, it is possible to display a blood vesselunder a mucosa even if there is a blood puddle in a body. FIG. 13 is adiagram for illustrating an example of an image obtained by picking upan image of a blood puddle portion on a mucosal surface in thenarrowband light observation mode. The blood puddle portion in the bodyis made of mixture of bleeding and water caused by treatment. In thewhite color light observation, such a blood puddle portion is observedonly in red color of the blood.

When a blood puddle portion 74 is observed in the narrowband lightobservation mode described above, a narrowband light near the wavelengthof 600 nm is transmitted through the blood 73 that includes the water ofthe blood puddle portion, and the blood vessel 61 under the mucosalsurface 71 a is displayed as shown in FIG. 13.

Therefore, when the mode is switched to the narrowband light observationmode during an operation, the blood vessel 61 under the mucosal surfaceunder the blood puddle portion can be seen on the observation monitor.

Next, processing by the image processing section 101 will be described.The image processing section 101 has the color conversion processingsection 101 b to execute color conversion processing.

(Color Conversion Processing by Image Processing Section)

Next, processing in the color conversion processing section 101 b willbe described. A first image signal P1 (λ1), a second image signal P2(λ2) and a third image signal P3 (λ3) are inputted to the colorconversion processing section 101 b.

FIG. 14 is a block diagram for illustrating a configuration of the imageprocessing section 101. Three image signals from the image pickup deviceare inputted to the color conversion processing section 101 b. The colorconversion processing section 101 b performs color conversion processingby allocation of channels for the first image signal P1 (λ1), the secondimage signal P2 (λ2) and the third image signal P3 (λ3) and outputs thesignals to the observation monitor 5.

In order to display the blood vessel 61 in a deep part with highcontrast by the narrowband light NL1 near the wavelength of 600 nm, thecolor conversion processing section 101 b allocates the first imagesignal P1 (λ1) to three channels of BGR to output the first image signalP1 (λ1) to the observation monitor 5 as a monochrome image. Note that,if there is a monochrome image display circuit, the first image signalP1 (λ1) may be inputted to the monochrome image display circuit tooutput the first image signal P1 (λ1) to the observation monitor 5 as amonochrome image.

As a result, the blood vessel 61 shown in FIG. 10 is monochromaticallydisplayed on the endoscopic image EI with high contrast in thenarrowband light observation mode. The blood flow BF in FIG. 11 and theblood vessel under the blood puddle in FIG. 13 are alsomonochromatically displayed with high contrast.

Thus, the image processing section 101 constitutes image output means oran image output section for outputting the first image signal P1 (λ1) onthe basis of an image signal obtained by picking up an image of a returnlight by the CCD 2 which is the image pickup means or the image pickupsection.

Note that the color conversion processing section 101 b may performcolor conversion processing using at least one of the second imagesignal P2 (λ2) and the third image signal P3 (λ3) in addition to thefirst image signal P1 (λ1). First to third modifications of the colorconversion processing by the color conversion processing section 101 bwill be described below.

First, the first modification will be described.

The color conversion processing section 101 b of the first modificationperforms processing of allocating the first image signal P1 (λ1), thesecond image signal P2 (λ2) and the third image signal P3 (λ3) to thechannels of G, R and B, respectively.

Here, for example, the color conversion processing section 101 bperforms processing of a following equation (12), and a luminance value1 mA (λ1) of the first image signal P1 (λ1), a luminance value Im (λ2)of the second image signal P2 (λ2) and a luminance value Im (λ3) of thethird image signal P3 (λ3) are allocated to the G, R and B channels,respectively.

$\begin{matrix}{\begin{pmatrix}B \\G \\R\end{pmatrix} = {\begin{pmatrix}1 & 0 & 0 \\0 & 1 & 0 \\0 & 0 & 1\end{pmatrix}\begin{pmatrix}{{Im}\left( {\lambda \; 3} \right)} \\{{ImA}\left( {\lambda \; 1} \right)} \\{{Im}\left( {\lambda \; 2} \right)}\end{pmatrix}}} & {{Equation}\mspace{14mu} (12)}\end{matrix}$

According to the equation (12), the relatively thick blood vessel 61 ina deep part is displayed in rather reddish color and is easy for thesurgeon to identify.

FIG. 15 is a diagram for illustrating a display example of an endoscopicimage using the three image signals. The blood vessel 61 in a deep partindicated by solid lines is displayed in rather reddish color; a bloodvessel 61A (indicated by dashed-dotted lines) in a deeper part than theblood vessel 61 is displayed in color from blue to black; and capillaryvessels 61B indicated by broken lines is displayed in almost yellow.Especially, a mucosa of living tissue and, further, blood on a mucosalsurface are also displayed in almost yellow.

Note that, though the third narrowband light NL3 is a light near thewavelength of 540 nm here, a blue light with a shorter wavelength, forexample, a light near a wavelength of 460 nm or 415 nm may be used toobtain epithelium information.

By allocating the narrowband light NL1 near the wavelength of 600 nmwith a high degree of absorption to the G channel and the narrowbandlight NL2 near the wavelength of 630 nm with a degree of absorptionlower than that of the narrowband light NL1 to the R channel, each ofthe blood vessel 61 and the blood vessel 61A can be displayed in color(rather reddish color) different from the color of the epithelium ofliving tissue.

Even if there is blood due to bleeding on the mucosal surface of livingtissue, the blood vessel 61 in a deep part and the blood vessel 61A in adeeper part are displayed in different color and, therefore, they areeasy for the surgeon to visually confirm.

When the three image signals are used, the bleeding point 72 describedwith reference to FIGS. 11 and 12 changes between yellow and orangealternately. This is because density (or concentration) of blood orthickness of a blood layer at the bleeding point 72 dynamically changesduring bleeding. At a place far from the bleeding point 72, since thedensity of blood or the thickness of the blood layer does notdynamically change, the color tone of blood remains yellow or orange.

As described above, when the three image signals are used, color tonesin an image change near the bleeding point 72, and, therefore, thesurgeon can easily recognize the bleeding point 72 by the change incolor tones. The surgeon can also recognize the thickness of the layerof the blood 73 by change between yellow and orange.

When the three image signals are used, an advantage also occurs that notonly noticeability of the blood vessels under bleeding described withreference to FIG. 13 but also noticeability of a foreign matter in bloodis improved. If light adjustment is performed with an R-channel bandsignal weighted most heavily, a foreign matter in blood is seen moreeasily than an image at the time of white light observation in thenormal light observation mode because the two narrowband lights near thewavelengths of 600 nm and 630 nm are easily transmitted through bloodbecause of their weak absorption characteristic. Since the twonarrowband lights near the wavelengths of 600 nm and 630 nm are easilytransmitted not only through blood but also through bile, urine and thelike, a foreign matter in or under such liquids is easily seen.

Note that the first image signal P1 (λ1), the second image signal P2(λ2) and the third image signal P3 (λ3) may be allocated to the G, B andR channels, respectively. In that case, by performing intensityadjustment and the like of each image signal, such as multiplication ofeach value of the matrix of the equation (12) by a coefficient, adisplay image similar to an image obtained by the color conversionprocessing of the above equation (12) can be displayed on theobservation monitor 5.

In the color conversion processing 101 b, a following equation (13) maybe used instead of the above equation (12).

$\begin{matrix}{\begin{pmatrix}B \\G \\R\end{pmatrix} = {\begin{pmatrix}1 & 0 & 0 \\1 & 0 & 0 \\0 & 1 & 0\end{pmatrix}\begin{pmatrix}{{Im}\left( {\lambda \; 3} \right)} \\{{ImA}\left( {\lambda \; 1} \right)} \\{{Im}\left( {\lambda \; 2} \right)}\end{pmatrix}}} & {{Equation}\mspace{14mu} (13)}\end{matrix}$

According to the equation (13), since the blood vessel 61 in a deep partis displayed in blue or bluish green as well as the capillary vessels inan epithelium being displayed reddish, the vessels can be easilyidentified by the surgeon.

Furthermore, note that a following equation (14) may be used instead ofthe above equation (12) in the color conversion processing 101 b.

$\begin{matrix}{\begin{pmatrix}B \\G \\R\end{pmatrix} = {\begin{pmatrix}1 & 0 & 0 \\0.5 & 0.5 & 0 \\0 & 1 & 0\end{pmatrix}\begin{pmatrix}{{Im}\left( {\lambda \; 3} \right)} \\{{ImA}\left( {\lambda \; 1} \right)} \\{{Im}\left( {\lambda \; 2} \right)}\end{pmatrix}}} & {{Equation}\mspace{14mu} (14)}\end{matrix}$

Furthermore, note that a following equation (15) may be used instead ofthe above equation (12) in the color conversion processing 101 b. Here,a takes a numerical value nearly from 1.0 to 1.5, β takes a numericalvalue nearly from 2.0 to 2.6, and γ takes a numerical value nearly from2.5 to 3.3 (for example, α:β:γ=0.56:1.00:1.17). In this case, sincecolor tone of a blood vessel in a deep part is blush green, and colortone of a mucosa is similar to that of normal observation, the surgeoncan perform observation without stress. By setting α, β and γ tonumerical values nearly from 2.3 to 2.7, nearly from 2.3 to 2.7, andnearly from 1.7 to 2.1, respectively (for example,α:β:γ=1.00:1.00:0.76), it becomes easy to observe blood vessels in anepithelium and a deep part.

$\begin{matrix}{\begin{pmatrix}B \\G \\R\end{pmatrix} = {\begin{pmatrix}\alpha & 0 & 0 \\\beta & 0 & 0 \\0 & \gamma & 0\end{pmatrix}\begin{pmatrix}{{Im}\left( {\lambda \; 3} \right)} \\{{ImA}\left( {\lambda \; 1} \right)} \\{{Im}\left( {\lambda \; 2} \right)}\end{pmatrix}}} & {{Equation}\mspace{14mu} (15)}\end{matrix}$

Note that another example of the channel allocation by the colorconversion processing section 101 b will be described. For example, atthe time of giving treatment, the narrowband light near the wavelengthof 540 nm, the narrowband light near the wavelength of 630 nm and thenarrowband light near the wavelength of 600 nm may be allocated to the Bchannel, the G channel and the R channel, respectively, instead of theabove equation (12).

At the time of giving a diagnosis, the narrowband light near thewavelength of 540 nm can be allocated to the B channel and the Gchannel, and the narrowband light near the wavelength of 600 nm or thenarrowband light near the wavelength of 630 nm can be allocated to the Rchannel.

Here, color balance adjustment will be described.

For example, in the case of allocating the narrowband light near thewavelength of 540 nm, the narrowband light near the wavelength of 630 nmand the narrowband light near the wavelength of 600 nm to the B channel,the G channel and the R channel, respectively, it is desirable toamplify the signal of the B channel relative to the signal of the Rchannel. The signal intensity of the narrowband light near thewavelength of 600 nm is not corrected, and the two signals of the signalof the narrowband light near a wavelength of 650 nm allocated to the Bchannel and the signal of the narrowband light near the wavelength of630 nm allocated to the R channel are adjusted so that the intensity ofthe former signal is 0.7 to 2.5 times as high as the intensity of thelatter signal. Note that the color conversion processing may beperformed after performing the color balance adjustment, or the colorbalance processing may be performed after the color conversionprocessing.

Thereby, color tone difference among a mucosa, fibrous tissue in a whitecolor tone, bleeding in yellow, a carbonized area in black, and a thickblood vessel in color tones from red to magenta becomes more remarkable,and it is possible to obtain a display image from which the surgeon cangive treatment or diagnosis more easily.

A color balance adjustment circuit for such color balance adjustment maybe provided for a previous stage of the W. B 25 in FIG. 1. In that case,when intensities of illumination lights of the narrowband light near thewavelength of 540 nm and the narrowband light near the wavelength of 630nm are almost equal to each other, the color balance adjustment circuitsets the signal of the narrowband light near the wavelength of 540 nmallocated to the B channel to be about 0.7 to 1.5 times, and the signalof the narrowband light near the wavelength of 630 nm to be about 0.6 to1.0 times.

Note that the color balance adjustment may be performed by the colorconversion processing section 101 b, or may be performed by the lightsource device 4 adjusting the intensities of the illumination lights, ormay be performed by adjusting transmittance of each color of the colorfilters of the image pickup device.

Next, a second modification will be described. Here, gain adjustment forcolor balance adjustment is not performed unless otherwise stated. Thatis, each gain is assumed to be 1.

In the second modification, channels are allocated to two image signalsamong the three image signals.

As an example, the color conversion processing section 101 b of thesecond modification may perform processing of allocating a first imagesignal P1 (λ1) to the G and B channels, and a second image signal P2(λ2) to the R channel.

In such allocation, in the endoscopic image EI, bleeding and a bloodvessel in a deep part are displayed in rather reddish color, a mucosa isdisplayed whitish, and capillary vessels in an epithelium are hardlydisplayed.

As a third modification, processing of allocating the first image signalP1 (λ1) to the R channel, and the third image signal P3 (λ3) to the Gand B channels may be performed in the color conversion processingsection 101 b.

In such allocation, in the endoscopic image EI, bleeding and a mucosaare displayed in rather reddish color, and a blood vessel in a deep partis displayed in greenish color.

In this case, gain adjustment of each channel may be performed. Forexample, if gains of the G and B channels to which the third imagesignal P3 (λ3) is allocated is set to be 1.3 to 1.5 times as much asgain of the R channel to which the first image signal P1 (λ1) isallocated, bleeding and a mucosa are displayed in reddish color, and ablood vessel in a deep part is displayed in color from bluish togreenish.

For example, if the gains of the G and B channels to which the thirdimage signal P3 (λ3) is allocated and the gain of the R channel to whichthe first image signal P1 (λ1) is allocated are set so that ascendingorder of gain is B, R and G, then bleeding and a mucosa are displayed inbrown, and a blood vessel in a deep part is displayed in color frombluish to greenish.

Furthermore, for example, if the gains of the G and B channels to whichthe third image signal P3 (λ3) is allocated and the gain of the Rchannel to which the first image signal P1 (λ1) is allocated are set sothat ascending order of gain is B, G and R, then bleeding and a mucosaare displayed in reddish color, and a blood vessels in a deep part isdisplayed in greenish color.

As described above, according to the embodiment described above, it ispossible to realize the endoscope apparatus 1 that displays a relativelythick blood vessel in a deep mucosa using the first image signal P1among the three image signals from the image pickup device 2.

That is, a narrowband light having an absorption characteristic asdescribed above, between a maximum value and minimum value of theabsorption characteristic of living tissue, as shown in FIG. 4 isradiated to a living mucosa, and, by an image of an obtained returnlight, a relatively thick blood vessel existing in a relatively deeppart of the living mucosa is emphasized and displayed on the screen ofthe observation monitor 5. Therefore, the surgeon can perform desiredtreatment such as ESD, looking at and confirming the relatively thickblood vessel.

If, using two or three image signals among the first to third imagesignals P1, P2 and P3, the color conversion processing section 101 ballocates channels to the first image signal P1, the second image signalP2 and the third image signal P3 and outputs the image signals to theobservation monitor 5, a relatively deep blood vessel, capillary vesselsin a mucosal epithelium and the like can be also displayed.

That is, in the endoscope apparatus 1 described above, a blood vesselexisting near an epithelium of living mucosa can be displayed with theuse of the third narrowband light NL3.

For example, since the third narrowband light NL3 near the wavelength of540 nm is used, a state of capillary vessels in an epithelium is alsodisplayed on the screen of the observation monitor 5 together with athick blood vessel. Furthermore, since the second narrowband light NL2near the wavelength of 630 nm is used, a state of a blood vessel in adeeper part is also displayed on the screen of the observation monitor 5together.

Thus, the surgeon can use an endoscopic image on the screen of theobservation monitor 5 not only for treatment but also for diagnosis ofliving tissue, for example, diagnosis of existence of cancer or rangediagnosis for identifying a range of cancer, and for discriminationdiagnosis for judging whether an affected part is benignant ormalignant, from a state of capillary vessels, for example, degree ofconcentration or dispersion of the capillary vessels. Furthermore, it ispossible to perform invasive depth diagnosis and the like taking intoaccount of a blood vessel in a deeper part.

Note that, though the light source device 4 described above generates anillumination light of a desired wavelength band using the xenon lamp 11,the rotating filter 14 and the like, in the endoscope apparatus 1, asindicated by dotted lines, the light source device 4 may be configuredto include a light emitting section 11A including a light emitting diodegroup 11 a including multiple light emitting diodes (LEDs) that emitdesired wavelength, for example, each of wavelengths of RGBcorresponding to the first filter group and each of wavelengths near 600nm and near 630 nm corresponding to the second filter group. In thatcase, the light emitting section 11A and the light guide 15 constitutean irradiating section that irradiates an subject with illuminationlight.

For example, in FIG. 1, instead of the xenon lamp 11, the heat ray cutfilter 12, the diaphragm device 13, the rotating filter 14 and the like,the light emitting section 11A indicated by a dotted line is provided inthe light source device 4. Furthermore, the light source device 4 isprovided with a driving circuit 11 b for driving each of the lightemitting diodes of the light emitting section 11A at predeterminedtimings according to each mode. The light emitting section 11A havingmultiple LEDs 11 a receives power source from the power supply 10 and iscontrolled and driven by the driving circuit 11 b under a control signalfrom the control circuit 17.

When the endoscope apparatus 1 is configured with the use of such alight source device, the same advantages as described above can be alsoobtained.

Note that the light emitting section 11A may employ a laser diode (LD)that emits predetermined multiple narrowband lights.

In the case where the light source device is mounted with any of a xenonlight source, an LED and an LD, and the CCD 2 is not a monochrome imagepickup device but is provided with RGB color filters or complementarycolor filters as the wavelength band limiting means or the wavelengthband limiting section that transmits the first narrowband light NL1,advantages equal to those described above can be obtained.

The second narrowband light NL2 shown in FIG. 4 may be a light of alonger wavelength band than the minimum value ACmin of the absorptioncharacteristic of hemoglobin (here, an absorption coefficient at thewavelength of 730 nm). That is, as for the wavelength of the secondnarrowband light NL2, such a wavelength band that the absorptioncoefficient is lower than the wavelength of the first narrowband lightNL1 and the scattering characteristic of living tissue is suppressed,for example, 740 nm, 770 nm, 805 nm, 810 nm, 850 nm, 870 nm, 880 nm, 910nm, 940 nm, 1020 nm or 1300 nm can be used to obtain advantages equal tothose described above (for example, when the narrowband light NL2 is setto any wavelength from 740 nm to 1300 nm, the narrowband light NL1 isset to any wavelength equal to or longer than 576 nm and at least equalto or shorter than 630 nm). Note that the second narrowband light NL2can be also generated even when any of a xenon light source, an LED andan LD is mounted as a light source device.

As described above, according to the present embodiment described above,it is possible to provide an endoscope apparatus capable of clearlydisplaying a blood vessel in a deep mucosa without complicated work ofmedicine administration being performed.

Second Embodiment

In the first embodiment, at least one narrowband light that includes thefirst narrowband light NL1 is actually radiated to living tissue as anillumination light, and the color conversion processing described aboveis performed for an image of a return light thereof. In the presentembodiment, however, the at least one narrowband light is not actuallyradiated to living tissue. Image information of a return light of eachnarrowband light is obtained by so-called spectral estimation, and colorconversion processing as described above is performed for a spectralimage signal of each wavelength obtained by the spectral estimation.That is, though the first narrowband light NL1 is generated by anillumination device having a rotating filter or a light emitting devicesuch as a light emitting diode, and color conversion processing isperformed for images of return lights thereof in the first embodimentdescribed above, an image signal corresponding to the first narrowbandlight NL1 is obtained by spectral estimation processing, and colorconversion processing is performed for a spectral estimation imagesignal obtained by the spectral estimation in the present embodiment.

FIG. 16 is a configuration diagram showing a configuration of anendoscope apparatus 1A according to the second embodiment of the presentinvention. In FIG. 16, the same components as shown in FIG. 1 aredenoted by the same reference numerals and signs and description thereofis omitted. Note that, in FIG. 16 also, a polarizing plate may bearranged on each of a front face of the CCD 2 and a front face of thelight guide 15 in a crossed Nichol prism state.

As shown in FIG. 16, a light source device 4A is configured, including alamp 11B that emits a white light, the heat ray cut filter 12, and thediaphragm device 13. An illumination light from the light source device4A is radiated to a subject via the light guide 15. Note that the lamp11B may emit a light other than a white color light.

An image pickup device 2A provided at the distal end of the insertionsection of the endoscope 3 is a color image pickup device. The imagepickup device 2A is, for example, a color CCD and includes RGB colorfilters on an image pickup surface. A return light from the subject isreceived by each pixel section of the image pickup surface via the RGBcolor filters, which are wavelength band limiting means or wavelengthband limiting sections, and image signals of three colors of RGB areoutputted from the image pickup device 2A.

A selector 100A outputs the three image signals of RGB to an imageprocessing section 101A. The image processing section 101A has aspectral estimation section, and, in the narrowband light observationmode, outputs a spectral estimation image signal near the wavelength of600 nm Here, in the narrowband light observation mode, the spectralimage estimation section of the image processing section 101A outputsthree image signals, more specifically, a spectral estimation imagesignal near the wavelength of 600 nm, a spectral estimation image signalnear the wavelength of 630 nm and a spectral estimation image signalnear the wavelength of 540 nm.

FIG. 17 is a diagram for illustrating a whole process flow in thenarrowband light observation according to the present embodiment. InFIG. 17, the same components as in FIG. 3 are denoted by the samereference numerals and signs and description thereof is omitted. Theimage processing section 101A includes a spectral estimation section 101c in addition to the color conversion processing section 101 b. That is,the image processing section 101A constitutes image output means or animage output section that generates and outputs a first image signal byperforming spectral estimation processing for an image pickup signal ofa return light. Here, the spectral estimation section 101 c extracts aspectral estimation image signal e1 near the wavelength of 600 nm, aspectral estimation image signal e2 near the wavelength of 630 nm and aspectral estimation image signal e3 near the wavelength of 540 nm fromthree images of RGB by spectral estimation processing and outputs thesignals to the color conversion processing section 101 b.

More specifically, the spectral estimation section 101 c calculatesn-dimensional spectral images from three inputs by matrix operations onthe basis of a priori information given in advance, and selectivelyoutputs e1, e2 and e3 among calculated n-dimensional spectral estimationimage signals. The spectral estimation section 101 c is configured tocalculate and output the spectral estimation image signal e1 near thewavelength of 600 nm, the spectral estimation image signal e2 near thewavelength of 630 nm and the spectral estimation image signal e3 nearthe wavelength of 540 nm using matrix operations and the like.

Subsequent processing in the color conversion processing section 101 bfor the first, second and third spectral estimation image signalsoutputted from the spectral estimation section 101 c is the same as theprocessing described in the first embodiment described above.

FIG. 18 is a diagram showing a spectral characteristic for illustratinga case of estimating the three narrowband-light spectral image signalse1, e2 and e3 from three broadband-light image signals B, G and R. Thethree broadband lights B, G and R in FIG. 18 are obtained by the colorfilters of the image pickup device 2A, and image signals of the threebroadband lights B, G and R are inputted to the spectral estimationsection 101 c.

The spectral estimation section 101 c estimates at least onenarrowband-light spectral estimation image signal e1 from the threebroadband-light image signals B, G and R by spectral estimationprocessing. Here, the spectral estimation image signal e1 near thewavelength of 600 nm, the spectral estimation image signal e2 near thewavelength of 630 nm and the spectral estimation image signal e3 nearthe wavelength of 540 nm are obtained from the broadband-light imagesignals B, G and R having wavelength bands as shown in FIG. 18 byspectral estimation processing. Here, two narrowband-light spectralestimation image signals e1 and e2 within the wavelength band R betweenthe maximum value ACmax and the minimum value ACmin in FIG. 4 and aspectral estimation image signal e3 outside the wavelength band R areobtained by spectral estimation, and the spectral estimation imagesignals e1, e2 and e3 are supplied to the color conversion processingsection 101 b.

Note that at least one spectral estimation image signal e1 (here, thethree spectral image signals e1, e2 and e3) may be obtained from imagesignals of two broadband lights among the three broadband lights, forexample, image signals of the broadband lights G and R by spectralestimation processing.

Furthermore, the spectral estimation image signal e1 (here, the threespectral estimation image signals e1, e2 and e3) may be obtained notfrom image signals of the broadband lights shown in FIG. 18 but fromimage signals of narrowband lights as shown in FIG. 19 by spectralestimation processing.

FIG. 19 is a diagram showing a spectral characteristic for illustratinga case of estimating spectral estimation image signals e1, e2 and e3 ofthe three narrowband lights from image signals of three narrowbandlights Bn, Gn and Rn. As shown in FIG. 19, the spectral estimationsection 101 c estimates the three spectral estimation image signals,that is, the spectral estimation image signal e1 near the wavelength of600 nm, the spectral estimation image signal e2 near the wavelength of630 nm and the spectral estimation image signal e3 near the wavelengthof 540 nm from the image signals Bn, Gn and Rn of the three narrowbandlights.

Note that at least one spectral estimation image signal e1 may beobtained from at least one narrowband light and at least one broadbandlight by spectral estimation. That is, at least one of the threebroadband lights in FIG. 18 may be a narrowband light, or at least oneof the three narrowband lights in FIG. 19 may be a broadband light.

The three narrowband lights Bn, Gn and Rn may be obtained by the colorfilters of the image pickup device 2A having a spectral characteristicas shown in FIG. 18 or FIG. 19, or may be obtained by applying returnlights of three illumination lights (that is, illumination lights of thenarrowband lights Bn, Gn and Rn) generated with the use of a rotatingfilter as shown in FIG. 2 in the light source device, to a monochromeimage pickup device.

Furthermore, note that image signals of the three (or two) broadbandlights may be obtained not with the use of the color filters of thecolor image pickup device but by applying return lights of three (ortwo) illumination lights generated by arranging a first group of filtersof a rotating filter having such a sensitivity characteristic that animage signal having a spectral characteristic as shown in FIG. 18 orFIG. 19 is obtained, on an optical path in the light source device, to amonochrome image pickup device.

Therefore, the same advantages as the endoscope apparatus 1 describedabove can be also obtained by the endoscope apparatus 1A of the presentembodiment.

FIG. 20 is a diagram for illustrating a flow of processing for an imageobtained from the image pickup device 2 in an image processing section101A according to the present embodiment.

As shown in FIG. 20, three images, that is, first to third image signalsP1, P2 and P3 are inputted to the spectral estimation section 101 c fromthe image pickup device 2. The spectral estimation section 101 cestimates and generates three spectral estimation image signals e1, e2and e3 from the inputted two or three image signals.

The color conversion processing section 101 b performs color conversionprocessing by allocation of channels, for the first spectral estimationimage signal e1, the second spectral estimation image signal e2 and thethird spectral estimation image signal e3 and outputs the signals to theobservation monitor 5.

Note that, as for the color filters provided on the surface of the imagepickup device, RGB color filters have been described as an example inthe present second embodiment, but the color filters may becomplementary color filters.

In the endoscope of the present embodiment also, a relatively thickblood vessel existing in a relatively deep part of a living mucosa isclearly displayed on the screen of the observation monitor 5 byperforming the color conversion processing described above. Therefore,the surgeon can perform desired treatment such as ESD, looking at andconfirming the relatively thick blood vessel.

Since the endoscope apparatus 1A described above is capable ofdisplaying a blood vessel existing in a part near the epithelium of aliving mucosa using the third spectral estimation image signal e3, thesurgeon can use an endoscopic image on the screen of the observationmonitor 5 not only for treatment but also for diagnosis of livingtissue, for example, diagnosis of existence of cancer or range diagnosisfor identifying a range of cancer, and for discrimination diagnosis forjudging whether an affected part is benignant or malignant, from a stateof capillary vessels, for example, degree of concentration or dispersionof the capillary vessels. Furthermore, it is possible to performinvasive depth diagnosis and the like taking into account of a bloodvessel in a deeper part.

The wavelength of the second spectral estimation image e2 shown in FIG.18 or FIG. 19 may be a light with a longer wavelength band than theminimum value ACmin of the absorption characteristic of hemoglobin inFIG. 4 (here, an absorption coefficient at the wavelength of 730 nm).That is, for the wavelength of the second spectral estimation image e2,such a wavelength band that the absorption coefficient is lower than thewavelength of the first spectral estimation image e1 and the scatteringcharacteristic of living tissue is suppressed, for example, 740 nm, 770nm, 805 nm, 810 nm, 850 nm, 870 nm, 880 nm, 910 nm, 940 nm, 1020 nm or1300 nm may be used to obtain advantages equal to those described above(for example, when the wavelength of the second spectral estimationimage e2 is set to any wavelength from 740 nm to 1300 nm, the wavelengthof the first spectral estimation image e1 is set to any wavelength equalto or longer than 576 nm and at least equal to or shorter than 630 nm).

Note that, in addition to the third spectral estimation image signal e3,fourth and fifth images obtained by further spectral estimation may beused, color-conversion processed and displayed on the observationmonitor 5.

As described above, according to the present embodiment described above,it is possible to provide an endoscope apparatus capable of clearlydisplaying a blood vessel in a deep mucosa without complicated work ofmedicine administration being performed.

Third Embodiment

In the first embodiment, at least one narrowband light that includes thefirst narrowband light NL1 is actually radiated to living tissue as anillumination light, and the color conversion processing described aboveis performed for an image of a return light thereof. In the secondembodiment, the three narrowband lights including the first narrowbandlight NL1 are not actually radiated to living tissue, but imageinformation of a return light of each narrowband light is obtained byso-called spectral estimation. Then, color conversion processing asdescribed above is performed for a spectral estimation image signal ofeach wavelength obtained by the spectral estimation. In the presentthird embodiment, the color conversion processing described above isperformed for an image signal of a return light of an actualillumination light of a narrowband light and a spectral estimation imagesignal obtained by spectral estimation.

A configuration of an endoscope apparatus 1B of the present embodimentis the same as the configuration of the endoscope apparatus 1 shown inFIG. 1, but a configuration of a rotating filter 14A of the presentembodiment is different. FIG. 21 is a diagram showing the configurationof the rotating filter 14A according to the present embodiment. As shownin FIG. 21, the rotating filter 14A is merely provided with RGB filtersections constituting a set of filters for outputting frame-sequentiallights having a spectral characteristic for the normal light observationmode. Return lights of the frame-sequential BGR lights are received by amonochrome image pickup device 2.

FIG. 22 is a diagram for describing a whole process flow in a speciallight observation mode according to the present embodiment. In FIG. 22,the same components as shown in FIG. 17 are denoted by the samereference numerals and signs and description thereof is omitted. Animage processing section 101B includes the color conversion processingsection 101 b and the spectral estimation section 101 c. The spectralestimation section 101 c generates at least one spectral estimationimage signal e from two or three image signals among RGB, and colorconversion processing for one image signal among RGB and the spectralestimation image signal is performed.

Here, more specifically, a first spectral estimation image signal e1near the wavelength of 600 nm and a third spectral estimation imagesignal e3 near the wavelength of 540 nm are estimated from the three (ortwo) image signals among RGB by spectral estimation and outputted to thecolor conversion section 101 b.

FIG. 23 is a diagram for illustrating a flow of processing for an imageobtained from the image pickup device 2 in the image processing section101B according to the present embodiment.

As shown in FIG. 23, three images, that is, first to third image signalsB, G and R are inputted to the spectral estimation section 101 c fromthe image pickup device 2. The spectral estimation section 101 cestimates and generates the two spectral estimation image signals e1 ande3 from the inputted two or three images.

The color conversion processing section 101 b performs color conversionprocessing by allocation of channels, for the spectral estimation imagesignal e1, the spectral estimation image signal e3 and the image signalR and outputs the signals to the observation monitor 5.

Note that the processing in the color conversion processing section 101b is similar to that of the first embodiment.

FIG. 24 is a diagram showing a spectral characteristic for illustratinga case of estimating at least one narrowband-light spectral estimationimage signal e1 from the three (or two) broadband-light image signals B,G and R. Note that, here, the two narrowband-light spectral estimationimage signals e1 and e3 are estimated from the three broadband-lightimage signals B, G and R.

Then, as shown in FIG. 23, the spectral estimation section 101 cperforms spectral estimation of and generates the spectral image signalse1 and e3 by signal processing on the basis of at least two image pickupsignals of return lights from a subject (here, the three image pickupsignals B, G and R).

The spectral estimation image signals e1 and e3 outputted from thespectral estimation section 101 c and the real image signal R areinputted to the color conversion processing section 101 b. As describedabove, the processing in the color conversion processing section 101 bis the same as the processing described in the above first embodiment.

Thus, if only the spectral image signal e1 obtained by spectralestimation is color-conversion-processed to be monochromaticallydisplayed as described above, a thick blood vessel 61 under a mucosa canbe clearly displayed. If at least one of the other two image signals,that is, the spectral estimation image signal e3 and the real imagesignal R, is included to be color-conversion-processed and displayed, itis possible to display not only the thick blood vessel 61 under a mucosabut also capillary vessels in an epithelium and a thick blood vessel ina deeper part on the observation monitor 5 together.

Note that, though the third image signal near the wavelength of 540 nmis obtained by spectral estimation in the example described above, thesecond image signal near the wavelength of 630 nm may be obtained byspectral estimation, and an image signal B may be used as a real image.

Furthermore, an illumination light for obtaining a real image signal maybe the narrowband light described with reference to FIG. 19.

Furthermore, note that the three broadband lights B, G and R in FIG. 23may be obtained by the color filters of the image pickup device 2A. Thatis, the three broadband lights B, G and R may be obtained with the useof the light source device 4A as described in the second embodiment andthe color filters of the image pickup device 2A.

Therefore, the same advantages as the endoscope apparatuses 1 and 1Adescribed above can be also obtained by the endoscope apparatus 1B ofthe present embodiment.

Note that, though RGB color filters have been described as an example ofa case of using color filters provided on the surface of the imagepickup device in the present third embodiment, the color filters may becomplementary color filters.

In the endoscope of the present embodiment also, a relatively thickblood vessel existing in a relatively deep part of a living mucosa isclearly displayed on the screen of the observation monitor 5 byperforming the processing described above. Therefore, the surgeon canperform desired treatment such as ESD, looking at and confirming therelatively thick blood vessel.

Since the endoscope apparatus 1A described above is capable ofdisplaying a blood vessel existing in a part near an epithelium of aliving mucosa using the spectral estimation image e3 corresponding tothe third narrowband light NL3 or the narrowband light Gn, the surgeoncan use an endoscopic image on the screen of the observation monitor 5not only for treatment but also for diagnosis of living tissue, forexample, diagnosis of existence of cancer or range diagnosis foridentifying a range of cancer, and for discrimination diagnosis forjudging whether an affected part is benignant or malignant, for example,from degree of concentration or dispersion of capillary vessels.Furthermore, it is possible to perform invasive depth diagnosis and thelike taking into account of a blood vessel in a deeper part.

The wavelength of the second narrowband light NL2 or the second spectralestimation image signal e2 may be a light of a longer wavelength bandthan the minimum value ACmin of the absorption characteristic ofhemoglobin in FIG. 4 (here, an absorption coefficient at the wavelengthof 730 nm). That is, as for the wavelength of the second narrowbandlight NL2 or the second spectral estimation image signal e2, such awavelength band that the absorption coefficient is lower than thewavelength of the first narrowband light NL1 or the first spectralestimation image signal e1 and the scattering characteristic of livingtissue is suppressed, for example, 740 nm, 770 nm, 805 nm, 810 nm, 850nm, 870 nm, 880 nm, 910 nm, 940 nm, 1020 nm or 1300 nm can be used toobtain advantages equal to those described above (for example, when thewavelength of the second narrowband light NL2 or the second spectralestimation image signal e2 is set to any wavelength from 740 nm to 1300nm, the wavelength of the first narrowband light NL1 or the firstspectral estimation image signal e1 is set to any wavelength equal to orlonger than 576 nm and equal to or shorter than 630 nm).

As described above, according to the present embodiment described above,it is possible to provide an endoscope apparatus capable of clearlydisplaying a blood vessel in a deep mucosa without complicated work ofmedicine administration being performed.

(Common Modification of Respective Embodiments) (First Modification)

In the three embodiments and each of modifications thereof describedabove, the light absorption characteristic of venous blood is given asan example, and two narrowband lights are selected on the basis of thecharacteristic. However, at least two narrowband lights as describedabove may be selected on the basis of the light absorptioncharacteristic of arterial blood or the light absorption characteristicof blood of combination of venous blood and arterial blood.

(Second Modification)

In the endoscope apparatus of each embodiment and each modification(including the modification of each embodiment) described above, thelight near the wavelength of 600 nm and the light near the wavelength of630 nm are used as the wavelengths of the first narrowband light NL1 andthe second narrowband light NL2, respectively. Preferably, the firstnarrowband light NL1 and the second narrowband light NL2 are anarrowband light with a wavelength within a wavelength range from 580 to620 nm having a distribution in a range of a predetermined width and anarrowband light with a wavelength within a wavelength range from 610 to730 nm having a distribution in a range of a predetermined width,respectively. More preferably, they are a narrowband light with awavelength within a wavelength range from 585 to 615 nm having adistribution in a range of a predetermined width and a narrowband lightwith a wavelength within a wavelength range from 620 to 640 nm having adistribution in a range of a predetermined width, respectively.

Therefore, if the first narrowband light NL1 and the second narrowbandlight NL2 are lights with wavelengths having an absorptioncharacteristic as described above between a maximum value and minimumvalue of absorption characteristic, the wavelengths of the firstnarrowband light NL1 and the second narrowband light NL2 are not limitedto the light near the wavelength of 600 nm and the light near thewavelength of 630 nm, respectively, and lights with any wavelength arepossible. For example, as the wavelengths of the first narrowband lightNL1 and the second narrowband light NL2, the light near the wavelengthof 610 nm and the light near a wavelength of 645 nm, or the light nearthe wavelength of 630 nm and the light near a wavelength of 660 nm maybe used, respectively.

(Third Modification)

In the endoscope apparatus of each embodiment and each modification(including the modification of each embodiment) described above, thelight near the wavelength of 540 nm is used to display capillary vesselsin an epithelium of living tissue, as the third narrowband light NL3.However, the wavelength of the third narrowband light NL3 is not limitedthereto. For example, as the wavelength of the third narrowband lightNL3, the light near the wavelength of 415 nm or 460 nm shorter than thewavelength 540 nm may be used. Especially, in order to obtaininformation about an epithelium of living tissue, the light near theshorter wavelength of 415 nm or 460 nm is more desirable than the lightnear the wavelength of 540 nm

(Fourth Modification)

It has been described that a heat light source lamp, an LED, an LD orthe like is used for the light source device of each embodiment and eachmodification (including the modification of each embodiment) describedabove. However, other means may be used. For example, a tunable lasermay be used as light source means or a light source section. A broadbandlight generated by exciting a fluorescent body with an LED or an LD maybe used.

(Fifth Modification)

In the case of radiating a narrowband light in the endoscope apparatusof each embodiment and each modification (including the modification ofeach embodiment) described above, it is possible to generate, forexample, the narrowband light near the wavelength of 600 nm by a laser,and the narrowband light near the wavelength of 630 nm by an LED. It isalso possible to generate the narrowband light near the wavelength of600 nm by an LED, and the narrowband light near the wavelength of 630 nmby a laser. By using a laser beam, it is possible to reduce noise in adepth direction.

(Sixth Modification)

In each embodiment and each modification (including the modification ofeach embodiment) described above, a relatively thick blood vessel in adeep mucosa is clearly displayed by an image of a narrowband light nearthe wavelength of 600 nm. In order to clearly display a blood vessel ina deeper part, it may be made possible to use an image of a narrowbandlight with a longer wavelength. Though display on the observationmonitor 5 is performed by the combination of the narrowband lights nearthe wavelength of 600 nm and near the wavelength of 630 nm describedabove, other combinations may be prepared in advance in that case sothat the surgeon can select a desired combination from among themultiple combinations.

As combinations of two display images, the endoscope 1 (or 1A, or 1B)has a first combination using a first image signal NL1 near thewavelength of 600 nm and a second image signal NL2 near the wavelengthof 630 nm and a second combination using a first image signal NL12 nearthe wavelength of 650 nm and a second image signal NL22 near awavelength of 680 nm, and the surgeon selects a desired combinationbetween the two combinations.

According to such a configuration, the surgeon can cause a blood vesselat a desired depth to be clearly displayed, changing the blood vesseldepth by selecting a combination and can cause a blood vessel in adeeper part to be displayed together by the second image signal toperform observation.

FIG. 25 is a diagram showing the light absorption characteristic ofvenous blood for illustrating the present sixth variation. In FIG. 25,one of the two combinations is a first combination of the narrowbandlight NL1 near the wavelength of 600 nm and the narrowband light NL2near the wavelength of 630 nm The other is a second combination of anarrowband light NL12 near the wavelength of 650 nm and a narrowbandlight NL22 near the wavelength of 680 nm The user can select whichcombination is to be selected. For example, the user can select by whichcombination display should be performed, by selecting a mode.

Note that, as another combination, a combination of a narrowband lightnear a wavelength of 615 nm and a narrowband light near the wavelengthof 645 nm, a combination of a narrowband light near the wavelength of630 nm and a narrowband light near the wavelength of 660 nm or the likeis possible.

In the case of the second combination, since the wavelength used isshifted to the long wavelength side in comparison with the firstcombination, an image of a deeper part is clearly displayed. Therefore,if blood, bile, urine or the like adheres to a mucosal surface of aliving body when the surgeon wants to display a blood vessel in a deeperpart, a blood vessel at a desired depth can be clearly displayed byselecting the second combination.

It is desirable that two wavelengths of the respective combinations havealmost the same wavelength difference so that similar contrast can beobtained.

Two or more combinations can be realized by increasing the number ofcombinations of rotating filters in the light source device orincreasing the number of spectral estimation image signals estimated byspectral estimation processing.

As combinations of narrowband light wavelengths, it is desirable to havetwo combinations of a combination of a narrowband light near awavelength of 580 nm and a narrowband light near the wavelength of 630nm, and a combination of a narrowband light near the wavelength of 590nm and a narrowband light near the wavelength of 630 nm in the case ofclearly displaying a blood vessel at a relatively shallow position froma mucosal surface.

As combinations of narrowband light wavelengths, it is desirable to havetwo combinations of a combination of a narrowband light near thewavelength of 600 nm and a narrowband light near the wavelength of 630nm, and a combination of a narrowband light near the wavelength of 650nm and a narrowband light near the wavelength of 680 nm in the case ofclearly displaying a blood vessel at a deeper position from a mucosalsurface or a blood vessel under a mucosa under blood or the like.

Though two combinations are used in the example described above, threeor more combinations are also possible. In the case of three, forexample, the three are a first combination of a narrowband light nearthe wavelength of 600 nm and a narrowband light near the wavelength of630 nm, a second combination of a narrowband light near the wavelengthof 650 nm and a narrowband light near the wavelength of 680 nm, and athird combination of a narrowband light near a wavelength of 700 nm anda narrowband light near the wavelength of 730 nm.

Since multiple display results can be obtained as described above, thesurgeon can cause a desired blood vessel to be clearly displayed byselecting a combination on a longer wavelength side (for example, acombination of narrowband lights near the wavelength of 650 nm and nearthe wavelength of 680 nm) when the concentration of blood or the likeadhering to a mucosal surface of a living body is high, and selecting acombination on a shorter wavelength side (for example, a combination ofnarrowband lights near the wavelength of 580 nm and near the wavelengthof 630 nm) when a blood vessel exists in a relatively shallow part orwhen the concentration of blood or the like adhering to a mucosalsurface of a living body is low.

(Seventh Modification)

In each embodiment and each modification (including the modification ofeach embodiment) described above, wavelength difference between twonarrowband lights of the first narrowband light NL1 and the secondnarrowband light NL2 is fixed. However, it is possible to cause one tobe fixed and the other to be variable.

For example, in the case of the narrowband light near the wavelength of600 nm and the narrowband light near the wavelength of 630 nm, it ispossible to fix the narrowband light near the wavelength of 600 nm andcause the other narrowband light to be variable from near the wavelengthof 630 nm to near the wavelength of 730 nm and set arbitrarily.Otherwise, it is also possible to fix the other narrowband light nearthe wavelength of 730 nm and cause a narrowband light from near thewavelength of 590 nm to near a wavelength of 620 nm to be variably andarbitrarily set. Note that it is also possible to fix the narrowbandlight near the wavelength of 600 nm and cause the other narrowband lightto be arbitrarily set in a wavelength band equal to or more than 730 nm.

By fixing one of wavelength differences of two narrowband lights andcausing the other to be variable, it is possible to display a bloodvessel in a desired area more clearly.

(Eighth Modification)

In each embodiment and each modification (including the modification ofeach embodiment) described above, three images are obtained to display anarrowband light image on the observation monitor 5. However, a fourthimage may be obtained so that a display image is generated byappropriately selecting images from among four images.

The endoscope apparatus has the narrowband light observation mode inaddition to the normal light observation mode, and the surgeon switchesthe normal light observation mode to the narrowband light observationmode as necessary to perform various treatments. By adding the fourthimage, it is possible to easily obtain a display image of eachobservation mode.

For example, a light source device capable of radiating an illuminationlight of a blue narrowband light (a broadband light is also possible)with a wavelength shorter than the wavelength of 540 nm is used toobtain the fourth image. The light source device alternately radiates anillumination light of a first combination of a light with the fourthwavelength and a narrowband light near the wavelength of 600 nm, and asecond combination of a narrowband light near the wavelength of 540 nmand a narrowband light near the wavelength of 630 nm to a subject. Notethat an illumination light of a combination of the light with the fourthwavelength, the narrowband light near the wavelength of 540 nm and thenarrowband light near the wavelength of 600 nm, and an illuminationlight of the narrowband light near the wavelength of 630 nm may bealternately radiated to a subject.

Then, a return light of each illumination light is received by the imagepickup device having the RGB color filters. For example, an image of areturn light with the fourth wavelength is picked up in the B band ofthe color filters, and an image of a return light of the narrowbandlight near the wavelength of 600 nm is picked up in the R band. Notethat the color filters of the image pickup device may be complementaryones. Furthermore, note that the image pickup device may be a monochromeimage pickup device.

Since images of the respective bands are separated from each other, fourmonochrome images are obtained in the video processor 7. Note thatappropriate color balance adjustment is performed for an image signal ofeach light to obtain each image.

Then, in the video processor 7, a normal image for the normal lightobservation mode is generated with the use of images of the four returnlights of the light with the fourth wavelength, the narrowband lightnear the wavelength of 540 nm, the narrowband light near the wavelengthof 600 nm and the narrowband light near the wavelength of 630 nm.

In the video processor 7, a first narrowband light image is generated byallocating an image signal of the light with the fourth wavelength tothe B and G channels, allocating an image signal of the narrowband lightnear the wavelength of 540 nm to the R channel, and using two images ofthe light with the fourth wavelength and the narrowband light near thewavelength of 540 nm.

Furthermore, in the video processor 7, a second narrowband light imageis generated with the use of three images of the narrowband light nearthe wavelength of 540 nm, the narrowband light near the wavelength of600 nm and the narrowband light near the wavelength of 630 nm.

Note that an image signal of the narrowband light near the wavelength of600 nm is displayed with high contrast.

Then, in response to an image display instruction by the surgeon, animage generated as described above is selected and displayed on theobservation monitor 5.

According to such a configuration, it is possible to display a normalimage for the normal light observation and a narrowband light image forthe narrowband light observation at the same time or display the normalimage and the narrowband light image being overlapped. For example, itis possible to display a normal light image and a first narrowband lightimage (or a second narrowband light image) in parallel or display thefirst narrowband light image and the second narrowband light image inparallel.

Furthermore, by allocating an image signal of the light with the fourthwavelength to the B channel, an image signal of the narrowband lightnear the wavelength of 540 nm to the G channel, and an image signal ofthe narrowband light near the wavelength of 600 nm to the R channel, orby allocating the image signal of the light with the fourth wavelengthto the B channel, the image signal of the narrowband light near thewavelength of 540 nm and the image signal of the narrowband light nearthe wavelength of 600 nm to the G channel, and the image signal of thenarrowband light near the wavelength of 600 nm (or the image signal ofthe narrowband light near the wavelength of 600 nm and an image signalof the narrowband light near the wavelength of 630 nm) to the R channel,it is possible to generate an overlap image obtained by addinginformation about a blood vessel in a deep part to a normal image anddisplay the image on the observation monitor 5.

Furthermore, by allocating the image signal of the light with the fourthwavelength to the B channel, the image signal of the light with thefourth wavelength and the image signal of the narrowband light near thewavelength of 600 nm to the G channel, and the image signal of thenarrowband light near the wavelength of 600 nm (or the image signal ofthe narrowband light near the wavelength of 600 nm and the image signalof the narrowband light near the wavelength of 630 nm) to the R channel,it is possible to generate an image in which both of a blood vessel inan epithelium and a blood vessel in a deep part are shown with highcontrast and display the image on the observation monitor 5.

Note that the image signal with the fourth wavelength may be generatedby spectral estimation.

As described above, according to the present eighth modification,parallel display or overlap display of a normal image and a narrowbandlight image becomes possible.

(Ninth Modification)

Furthermore, the endoscope apparatus according to each embodiment andeach modification (including the modification of each embodiment)described above may be used to cause a normal light image for the normallight observation mode and a narrowband light image for the narrowbandlight observation mode to be displayed in parallel.

For example, in the case of performing treatment such as ESD, anarrowband light image for the narrowband light observation mode forclearly displaying a thick blood vessel in a deep mucosa can bedisplayed on the observation monitor 5 after the surgeon identifies alesioned part until the lesioned part is dissected and ablated. Notethat, after the surgeon identifies a lesioned part until he dissects andablates the lesioned part, a narrowband light image for the narrowbandlight observation mode and a normal light image for the normal lightobservation mode may be displayed on the observation monitor 5 inparallel.

The surgeon performs hemostasis treatment, looking at a narrowband lightimage (or parallel display of a narrowband light image and a normallight image) displayed on the observation monitor 5. As described above,there may be a bleeding point under blood during bleeding. Therefore,there may be a case where it is better to perform hemostasis treatment,looking at a narrowband light image.

When a narrowband light image and a normal light image are displayed inparallel, the surgeon can confirm a state of hemostasis after finishingthe hemostasis treatment, looking at the normal light image. When onlythe narrowband light image is displayed, the surgeon can confirm thestate of hemostasis after finishing the hemostasis treatment by changingthe mode of the endoscope apparatus to the normal light observation modeand displaying the normal light image on the observation monitor 5.

Conventionally, normal light observation by an image under a white colorlight and conventional narrowband light observation using narrowbandlights near the wavelengths of 415 nm and 540 nm have been performed. Byadding the new narrowband light observation mode for clearly displayinga blood vessel in a deep mucosa according to each embodiment and eachmodification (including the modification of each embodiment) describedabove, it is possible to perform, for example, invasive depth diagnosisof a lesion more effectively.

In endoscope diagnosis, observation of a lesioned part is performed.There may be a case where, while a normal light image or a conventionalnarrowband light image (an image corresponding to narrowband lights nearthe wavelengths of 415 nm and 540 nm) is displayed on the observationmonitor 5, a lesioned part is enlargedly displayed to perform invasivedepth diagnosis of the lesion.

In this case, conventionally, the surgeon enlarges the conventionalnarrowband light image (the image corresponding to the narrowband lightsnear the wavelengths of 415 nm and 540 nm) to perform the invasive depthdiagnosis of the lesion.

However, by causing a new narrowband light image to be displayed on theobservation monitor 5 together with the conventional narrowband lightimage using the endoscope apparatus according to each embodiment andeach modification (including the modification of each embodiment)described above, the surgeon can perform the invasive depth diagnosis ofthe lesion with a higher accuracy.

FIG. 26 is a diagram for illustrating an example of transition of imagedisplay during enlargement observation of the ninth modification. First,the surgeon performs observation or diagnosis of a lesioned part,displaying a normal light image or a conventional narrowband light image(an image corresponding to narrowband lights near the wavelengths of 415nm and 540 nm) EI1 on the observation monitor 5. It is possible not onlyto, by specifying enlarged display during the diagnosis, display anenlarged conventional narrowband light image (the image corresponding tothe narrowband lights near the wavelengths of 415 nm and 540 nm) EI2 onthe observation monitor 5 but also to display the conventionalnarrowband light image (the image corresponding to the narrowband lightsnear the wavelengths of 415 nm and 540 nm) EI1 and an image EI3 whichincludes the new narrowband light image (for example, an imagecorresponding to a narrowband light near the wavelength of 600 nm) bythe surgeon's instruction.

This image EI3 may be an image in which the conventional narrowbandlight image (the image corresponding to the narrowband lights near thewavelengths of 415 nm and 540 nm) and the new narrowband light image(for example, an image corresponding to a narrowband light near thewavelength of 600 nm) are displayed in parallel or may be an image inwhich the conventional narrowband light image (the image correspondingto the narrowband lights near the wavelengths of 415 nm and 540 nm) andthe new narrowband light image (for example, an image corresponding to anarrowband light near the wavelength of 600 nm) are overlappedlydisplayed.

Since the image EI3 includes an image of a blood vessel at a positiondeeper from a mucosal surface, the surgeon can perform invasive depthdiagnosis of a lesion such as cancer with a higher accuracy.

As described above, according to each embodiment and each modification(including the modification of each embodiment) described above, it ispossible to provide an endoscope apparatus capable of clearly displayinga blood vessel in a deep part of a mucosa without complicated work ofmedicine administration being performed.

The present invention is not limited to the embodiments described above,and various changes, alterations and the like are possible within arange not changing the spirit of the present invention.

What is claimed is:
 1. An endoscope apparatus comprising: anillumination section radiating at least one or more illumination lightshaving a predetermined wavelength band to a part under an epithelium ofa living mucosa of a subject; an image pickup section picking up animage of a return light from the part under the epithelium of the livingmucosa based on radiation of the illumination section; an image outputsection outputting a signal corresponding to a first wavelength bandhaving a narrowband spectral characteristic and a signal correspondingto a second wavelength band having a lower absorption coefficient of ahemoglobin absorption characteristic than an absorption coefficient of ahemoglobin absorption characteristic of the signal corresponding to thefirst wavelength band and having such a spectral characteristic that ascattering characteristic of the living tissue is suppressed, in a redband in a visible range, which is between a wavelength band including amaximum value and a wavelength band including a minimum value withregard to the hemoglobin absorption characteristic of the living tissueof the subject, after image pickup by the image pickup section; and adisplay section displaying an image on the basis of the signalcorresponding to the first wavelength band and the signal correspondingto the second wavelength band.
 2. The endoscope apparatus according toclaim 1, wherein the image output section also outputs a signalcorresponding to a third wavelength band, the signal being on a shorterwavelength side relative to the red band in the visible range and havingthe narrowband light spectral characteristic in order to obtainepithelium information about the living mucosa; and the endoscopeapparatus further comprises a color conversion processing sectionallocating signals outputted from the image output section to respectivecolor channels of BGR, the signals being given a predeterminedcoefficient.
 3. The endoscope apparatus according to claim 2, wherein ina case of allocating the signal corresponding to the third wavelengthband to a B channel, the signal corresponding to the first wavelengthband to a G channel, and the signal corresponding to the secondwavelength band to an R channel, the color conversion processing sectiongives the predetermined coefficient in a manner that the signal of the Bchannel is amplified relative to the signal of the R channel.
 4. Theendoscope apparatus according to claim 1, wherein the illuminationsection radiates the illumination light via a band limiting sectionlimiting a wavelength band to the first wavelength band and the secondwavelength band; and the image output section outputs the signalcorresponding to the first wavelength band and the signal correspondingto the second wavelength band on the basis of an image signal obtainedby picking up an image of the return light by the image pickup section.5. The endoscope apparatus according to claim 1, wherein the imagepickup section receives and picks up an image of the return light via aband limiting section limiting a wavelength band to the first wavelengthband; and the image output section outputs the signal corresponding tothe first wavelength band and the signal corresponding to the secondwavelength band on the basis of an image signal obtained by picking upan image of the return light by the image pickup section.
 6. Theendoscope apparatus according to claim 1, wherein the image outputsection generates and outputs the signal corresponding to the firstwavelength band by performing spectral estimation processing for animage pickup signal of the return light.
 7. The endoscope apparatusaccording to claim 1, wherein the first wavelength band is such awavelength band that a difference between light transmittances of acapillary vessel in the living mucosa of the subject and a blood vesselhaving a longer diameter than the capillary vessel is a predeterminedvalue or more.
 8. The endoscope apparatus according to claim 1, whereinthe first wavelength band has a peak wavelength of the spectralcharacteristic within a range from a wavelength of 585 nm to awavelength of 615 nm.
 9. The endoscope apparatus according to claim 1,wherein the image output section generates and outputs the signalcorresponding to the second wavelength band by performing spectralestimation processing for a wavelength band having a peak wavelength ofthe spectral characteristic and being different from the firstwavelength band.
 10. The endoscope apparatus according to claim 1,wherein the second wavelength band has a peak wavelength of the spectralcharacteristic within a range from a wavelength of 610 nm to awavelength of 730 nm.
 11. The endoscope apparatus according to claim 1,wherein the second wavelength band has a peak wavelength of the spectralcharacteristic in wavelength bands after the wavelength of 730 nm. 12.The endoscope apparatus according to claim 2, wherein the thirdwavelength band has a peak wavelength of the spectral characteristicwithin a range from a wavelength of 400 nm to a wavelength of 585 nm.13. The endoscope apparatus according to claim 1, wherein the endoscopeapparatus has a normal light observation mode and a narrowband lightobservation mode; and the image output section outputs the signalcorresponding to the first wavelength band and the signal correspondingto the second wavelength band in the narrowband light observation mode.